Question for computer geeks

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I am having trouble on my two office computers and I need help figuring it out.

The basic problem is intermittently both computers (they are networked together by a wired network and router) will slow down to a snail's pace. One keystroke will take a few seconds to show up on the screen, closing or opening a window will take 5 seconds.

I ran a virus scan, two spyware scans and I defragged both hard drives. The problem is still happening.

The slowdown happens when I run one program which is an office scheduling and records program. This program is running all day long. I need to figure out if it a problem with the program, or a problem with something else slowing the computer down. I contacted the vendor for my program and they have looked at it and can't find anything wrong.

Is there a program I can run to see how fast my computer is running at any given time, and how much memory it is using up? Then when my computer slows down, I could run this program, and it will help me figure out what is slowing my computer down.